Antonio Parancin, a weather forecaster from North Coast Storm Chasers, said today's conditions were "almost a direct copy of yesterday's conditions".

"Thunderstorms are expected to develop after lunch and then quickly strengthen into severe storms that may become supercells and track in a general NE direction," he posted on Facebook

"This is exactly what happened yesterday when a severe supercell tracked from south of Yamba all the way through Ballina and Byron Bay delivering giant hailstones and destructive winds.

"Today my personal hot spot for severe activity is from Coffs to Casino to Ballina to Byron and all surround areas."

Severe thunderstorms that develop today are likely to contain:

Damaging / destructive winds

Large to giant hailstones

Intense rainfall and reduced visibility

Flash flooding

Frequent lightning

Green in clouds (hail present).

Mr Parancin said the storms would not take long to fire up and gain strength.

"Some things to mention: Do not park you car under a tree because if a branch snaps and hits your car it will be worse than if hail had affected it, instead bring out the doona if you must," he wrote on Facebook.

"Do not stand outside when active lightning is occurring, yesterday we had many reports of very close calls, you don't want to be barbecued."